This invention relates generally to image recording apparatuses such as a printer, a copying machine and so on, and more particularly, to an image recording medium such as, for example, a developing sheet, a photo-sensitive sheet, a heat-sensitive sheet or the like for use with the image recording apparatuses and also to a detecting device for the image recording medium.
Image recording medium material is known from Japanese Patent Application Laid-Open Nos. 58-88739, 58-88740, 61-42649, 61-24495 and the like. The known image recording medium material consists of a combination of two types of recording media. One type is a recording medium coated with microcapsules which contain chiefly photo-curable material, photo-polymerization initiator and dye precursor. The other type is a image recording medium coated with developing agent which reacts with the dye precursor contained in the microcapsules, to develop color.
In the image recording medium material of the kind referred to above, the microcapsules containing the photo-curable material are cured selectively by light, and the cured microcapsules increase in mechanical strength. The image recording medium material is used with an image recording apparatus in such a manner that the recording medium coated with the microcapsules is exposed to light in accordance with image information, and the microcapsules not cured by the exposure are destroyed to cause the dye precursor contained in the uncured microcapsules to react with the developing agent coated with the image recording medium, thereby recording an image onto the image recording medium.
The image recording medium is composed of a white sheet-like carrier or substrate and white developing agent coated on the substrate. However, the image recording medium has no identifying index indicative of whether or not one side of the image recording medium is coated with the developing agent. It is very difficult for a user to identify the developing-agent-coated side of the image recording medium. When the image recording medium is used with the above-described image recording apparatus, there may often occur a case where the image recording medium is erroneously inserted in the apparatus with the developing-agent-coated side of the image recording medium facing incorrectly. It is of course that erroneous insertion of the image recording medium does not enable the image to be recorded onto the image recording medium.
Apart from the above, in general, the conventional image recording apparatus employs mechanical means such as microswitches or the like, in order to detect presence and absence of a sheet-like image recording medium such as a developing sheet, a heat-sensitive sheet or the like having front and back sides distinguishable from each other.
Further, the usual image recording apparatus is not provided with means for identifying the front and back sides of the image recording medium. When a user feeds the image recording medium into the apparatus, the user ascertains the front and back sides of the image recording medium with his eyes, and sets the image recording medium in the apparatus so as to face correctly or appropriately.
In connection with the above, a general or usual way of identifying the front and back sides of the image recording medium relies upon optical means, as disclosed in Japanese Patent Application Laid-Open Nos. 58-205572 and 57-70905.
It is desirable for the image recording apparatus, however, to have means for identifying the front and back sides of the image recording medium, in order to lighten the user's burden and to prevent errors in printing or development due to erroneous feeding of the image recording medium.
As discussed above, it is required for the conventional arrangement to have both the mechanical means and the optical means independently of each other in order to identify the presence and absence and the front and back sides of the image recording medium. This results in an increase in the cost.